Catalytic converters may be provided to control exhaust emissions for a vehicle, however as the fuel-to-air ratio of the vehicle varies to rich or lean conditions, the state of the catalyst may decrease its effectiveness in preventing harmful emissions, such as CO or NOx from entering the atmosphere. Oxygen sensors may be provided to determine the state of a catalyst; however, this may not provide a quick response to dynamic operation state changes, resulting in harmful emissions being released during transitional operation states.
The inventors have recognized the issues with the above approach and offer a method and system to at least partly address them. In one embodiment, a method is provided for controlling an engine exhaust with an upstream sensor and a downstream sensor. The method comprises adjusting a set-point for the downstream sensor based on a rate of change of air mass flow upstream of the engine and adjusting fuel injection to control exhaust fuel-air ratio (FAR) at the downstream sensor to the adjusted set-point, and to control exhaust FAR at the upstream sensor to an upstream sensor set-point.
In this way, the catalyst state can be monitored and fuel injection can be adjusted to ensure the catalyst does not exceed a threshold amount of oxidants or reductants by predicting probable lean or rich FAR conditions. The present disclosure may offer several advantages. For example, preventing catalyst oxidant or reductant saturation reduces CO and NOx emissions and enhances fuel economy.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.